Wireless communication systems are widely deployed to provide various types of communication content, such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-input-single-output, multiple-input-single-output or a multiple-input-multiple-output (MIMO) system.
Third-generation networks and user equipments (UE) are widely used throughout the world. Inter system handover between Global System for Mobile Communications (GSM) and Universal Terrestrial Radio Access Network (UTRAN) are expected to play an increasingly important role, as many third-generation UEs will be dual-mode UE capable of performing in both Generalized Packet Radio Services (GPRS) networks and Evolved UMTS Terrestrial Radio Access networks (E-UTRAN). Each time such a dual-mode UE moves between the two networks, an inter-system handover (i.e., inter-RAT (radio access technology)) is performed. For example, an inter-RAT handover to E-UTRAN procedure may hand the UE over from a GSM system to an E-UTRAN system. Therefore, a plurality of different RATs, such as TDMA, WCDMA, CDMA2000 and WLAN may coexist in one geographical area.
In order to enable almost seamless services for the end-users, third generation dual-mode UEs may be able to communicate with two RATs. As a result, both the UE and the radio access network have to be able to support handover between the two technologies.
Various problems are associated with such inter-RAT handovers, typically due to the inherent differences in the radio access technologies. For instance, in GPRS and UMTS, a UE may support up to eleven packet data protocol (PDP) contexts. A PDP context contains a user's session information and is registered in the Gateway GPRS Support Node (GGSN) in a GPRS system. If a dual-mode UE performs an inter-RAT handover from, for instance, either a GPRS system or a UMTS system, to E-UTRAN, the PDP contexts are translated into evolved packet system (EPS) bearers in the long term evolution (LTE) evolved packet core (EPC) system via a one-to-one mapping. The EPC core-network specifications for an LTE system require that a UE support eleven EPS bearers. In the LTE access network, EPS bearers are subsequently mapped one-to-one to data radio bearers (DRB). This causes a misalignment between the numbers of bearers supported by different stratum of the LTE system since the specifications for the radio resource control layer of the UE mandate only that the UE support eight DRBs.
Therefore, there is a need in the art for a technique for handling the mismatch between the numbers of bearers supported in different stratum of a radio access technology, such as an LTE system.